1. Field of the Invention
The present invention relates to temperature control apparatus. In particular, the present invention relates to a thermostat which automatically provides changeover between heating and cooling.
2. Description of the Prior Art
With the dramatic increase in energy costs in recent years, and the growing concern over the availability of fuels, increased attention has been focused upon energy conservation. The reduction of energy consumption in home heating has been a topic of widespread interest.
Significant energy saving in home heating can be achieved by the use of temperature setback at one or more periods during each day. For example, by decreasing the control temperature setting of a thermostat during sleeping hours and during times of day when no one is at home, significant energy savings can be achieved. Clock thermostats which provide at least one setback period have been available for many years. Until recently, these clock thermostats have generally been of a mechanical or electromechanical type.
With the recent development of microprocessors and microcomputers, computerized thermostats which automatically provide two or more setback and setup temperature periods have been developed. Among manufacturers of computerized thermostats are Autotronics, Inc., Control Pak Corporation, Honeywell, Inc., Micro Display Systems, Inc., PSG Industries, Inc., RapidCircuit Corp., and Texas Instruments. A description of computerized thermostats available from these manufacturers may be found in Popular Science, "Computerized thermostats program your comfort and save on energy costs", pages 104-106 (October 1979).
Other digital thermostats or process control apparatus are disclosed in the following U.S. patents:
Bunting: No. 3,912,913 PA1 Stephenson: No 4,001,557 PA1 Marooka et al: No. 4,004,138 PA1 Hall: No. 4,071,745 PA1 Wong: No. 4,079,366 PA1 Wyland: No. 4,110,632 PA1 Balduzzi et al: 4,162,036
In Bunting Pat. No. 3,912,913, a process control apparatus is disclosed which includes a digital computer. Digital temperature values from a temperature register are compared with values from a temperature sensor. A program which may be coded on a punch card or tape is read by a program reader and is used to control the arithmetic unit and provide selection of the proper temperature from the temperature register at the appropriate times.
The Stephenson Pat. No. 4,001,557 shows a digital process controller having a timing clock which is used in conjunction with programmable read only memories. A specific embodiment shown by Stephenson shows temperature being varied as a function of time, together with auxiliary control of a vacuum pump and a gas pump.
In the Marooka et al Pat. No. 4,004,138, a temperature control for a steel furnace is shown. The control utilizes various arithmetic units and a temperature decision unit to control temperatures in various zones of the steel furnace.
The Hall Pat. No. 4,071,745 shows a microprocessor controlled electronic thermostat. The values of the reference temperatures and times are programmable and changeable by the user. In addition, hysteresis and anticipation values are stored. Zone control of multiple zones is also illustrated in the Hall patent.
The Wong Pat. No. 4,079,366 shows a digital thermostat which includes digital memories, a keyboard and a display. The user may program in any desired temperature and time. Hysteresis is adjustable in the digital thermostat of the Wong patent. In addition, day off selectors are provided so that weekends can have a different time/temperature program.
The Wyland Pat. No. 4,110,632 shows a device which monitors indoor and outdoor temperatures together with a time count from a seven-day counter. The purpose of the device is to disconnect selective loads when conditions of peak electrical use are likely to occur.
The Balduzzi et al Pat. No. 4,162,036 shows a solid state thermostat having a pair of potentiometers R.sub.d and R.sub.v controlled by knobs 13 and 14 to provide set points for high and low temperatures. One or the other of these two potentiometers is switched into a bridge by switches S1 and S2. These switches are controlled by flipflop FF4, which in turn is controlled by Clock 1 and Clock 2. When one of the clock settings is reached, it triggers FF4 which in turn selects the appropriate switch S1 or S2.
Although there has been considerable recent activity in the development of digital computerized thermostats, there is a continuing need for improvement. One shortcoming of both the prior art electro-mechanical thermostats and the more recently developed digital computerized thermostats is that the changeover from heating to air conditioning and vice versa is performed manually by a control switch or the like. This is inconvenient particularly in those climates having hot days and cool nights, where air conditioning is required during the daylight hours and heating is required at night.
In addition, in the prior art digital computerized thermostats, the air conditioning program has typically not been independent of the heat program. As a result, when the user manually switches from a heat program to an air conditioning program, re-programming of the thermostat has been required and/or the heat program has been lost. Similar problems occur each time a changeover is made back from the air conditioning program to the heat program.